The tsll and BN51 genes were originally identified by genetic methods in mammalian cell cycle temperature sensitive mutants and are absolutely required for cell cycle traverse. The human analogs of these genes have recently been cloned. The mRNA levels of tsll and BN51 are induced during the transition of cells from a non-proliferative (Go) state to S with kinetics that are clearly different from those in the induction of c-myc and c-fos. It is likely that transcription of these genes is regulated in other contexts as well, e.g. during the cell cycle and during terminal differentiation. The goal of the proposed project is to determine the parameters which govern transcriptional regulation of these genes in order to elucidate the molecular mechanisms which control the progression of the mammalian cell cycle. this will be accomplished by a variety of in vitro techniques outlined as follows: 1) An in vitro transcription system will be established in soluble nuclear extracts of cells which demonstrate transcription regulation of these genes. This analysis includes the construction of deletion mutant templates to identify those elements necessary for the regulated expression of these genes. 2) In vitro protein-DNA binding studies will be employed to identify regulatory factors that specifically interact with critical regions of the promoter (or enhancer). 3) Regulatory factors identified by these methods will be purified to prepare reagents (e.g. antibodies and cDNAs) which will be used to determine the mechanism by which they are able to activate the transcription of tsll or BN51. 4) Regulatory factors identified in different contexts (e.g. during the cell cycle and differentiation) will be compared to identify alternate pathways which may operate in the regulation of these genes. It is the goal of these studies to identify molecular components of a regulatory pathway(s) which operates in the control of cell proliferation and the mammalian cell cycle. As such, this work has a direct bearing on problems related to oncogenesis where such regulatory mechanisms are aberrant, and thus may aid in the understanding of this process.